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          <h1 class="post-title" itemprop="name headline">hadoop基础概念</h1>
        

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        <p>hadoop基础概念，介绍HDFS的优缺点，以及读写流程。<br><a id="more"></a></p>
<h2 id="hadoop基础演练"><a href="#hadoop基础演练" class="headerlink" title="hadoop基础演练"></a>hadoop基础演练</h2><h3 id="慕课网视频"><a href="#慕课网视频" class="headerlink" title="慕课网视频"></a>慕课网视频</h3><ul>
<li><a href="https://www.imooc.com/video/16284" target="_blank" rel="noopener">hadoop基础演练</a></li>
</ul>
<p>通过该视频了解下基本知识。</p>
<h2 id="知识整理"><a href="#知识整理" class="headerlink" title="知识整理"></a>知识整理</h2><h3 id="HDFS概念"><a href="#HDFS概念" class="headerlink" title="HDFS概念"></a>HDFS概念</h3><ul>
<li>数据块<ul>
<li>抽象块而非整个文件作为存储单元，屏蔽了文件的概念，文件分块</li>
<li>默认大小为64MB，一般设置为128M，备份X3</li>
</ul>
</li>
<li>NameNode（主，一个NameNode，多个DataNode）<ul>
<li>管理文件系统的命名空间，存放文件元数据</li>
<li>维护着文件系统的所有文件和目录，文件与数据块的映射</li>
<li>记录每个文件中各个块所在数据节点的信息</li>
</ul>
</li>
<li>DataNode（从，一个NameNode，多个DataNode）<ul>
<li>存储并检索数据块</li>
<li>向NameNode更新所存储块的列表</li>
</ul>
</li>
</ul>
<h3 id="HDFS的优缺点"><a href="#HDFS的优缺点" class="headerlink" title="HDFS的优缺点"></a>HDFS的优缺点</h3><h4 id="优点"><a href="#优点" class="headerlink" title="优点"></a>优点</h4><ul>
<li>适合大文件存储，支持TB、PB级的数据存储，并有副本策略</li>
<li>适合大文件存储，支持TB、PB级的数据存储，并有副本策略</li>
<li>支持流式数据访问，一次写入，多次读取最高效</li>
</ul>
<h4 id="缺点"><a href="#缺点" class="headerlink" title="缺点"></a>缺点</h4><ul>
<li>不适合大量小文件存储</li>
<li>不适合并发写入，不支持随机文件修改</li>
<li>不支持随机读等低延时的访问方式</li>
</ul>
<h3 id="HDFS的读写流程"><a href="#HDFS的读写流程" class="headerlink" title="HDFS的读写流程"></a>HDFS的读写流程</h3><h4 id="HDFS写流程"><a href="#HDFS写流程" class="headerlink" title="HDFS写流程"></a>HDFS写流程</h4><ol>
<li>客户端向NameNode发起写数据请求</li>
<li>分块写入DataNode节点，DataNode自动完成副本备份</li>
<li>DataNode向NameNode汇报存储完成，NameNode通知客户端</li>
</ol>
<h4 id="HDFS读流程"><a href="#HDFS读流程" class="headerlink" title="HDFS读流程"></a>HDFS读流程</h4><ol>
<li>客户端向NameNode发起读数据请求</li>
<li>NameNode找出距离最近的DataNode节点信息</li>
<li>客户端从DataNode分块下载文件</li>
</ol>

      
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              <div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-2"><a class="nav-link" href="#hadoop基础演练"><span class="nav-number">1.</span> <span class="nav-text">hadoop基础演练</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#慕课网视频"><span class="nav-number">1.1.</span> <span class="nav-text">慕课网视频</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#知识整理"><span class="nav-number">2.</span> <span class="nav-text">知识整理</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#HDFS概念"><span class="nav-number">2.1.</span> <span class="nav-text">HDFS概念</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#HDFS的优缺点"><span class="nav-number">2.2.</span> <span class="nav-text">HDFS的优缺点</span></a><ol class="nav-child"><li class="nav-item nav-level-4"><a class="nav-link" href="#优点"><span class="nav-number">2.2.1.</span> <span class="nav-text">优点</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#缺点"><span class="nav-number">2.2.2.</span> <span class="nav-text">缺点</span></a></li></ol></li><li class="nav-item nav-level-3"><a class="nav-link" href="#HDFS的读写流程"><span class="nav-number">2.3.</span> <span class="nav-text">HDFS的读写流程</span></a><ol class="nav-child"><li class="nav-item nav-level-4"><a class="nav-link" href="#HDFS写流程"><span class="nav-number">2.3.1.</span> <span class="nav-text">HDFS写流程</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#HDFS读流程"><span class="nav-number">2.3.2.</span> <span class="nav-text">HDFS读流程</span></a></li></ol></li></ol></li></ol></div>
            

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